Modern high speed networking protocols provide both quality of service and bandwidth guarantees to every transport connection established across the network. Such guarantees are achieved by means of an integrated set of procedures. One of the major inputs to this set of integrated procedures is an accurate but simple characterization of the connection traffic offered to the network.
In such high speed packet switching networks, many different classes of traffic share the common transmission resources. The network must therefore be capable of providing traffic generated by a wide range of multimedia services such as text, image, voice and video. The traffic characteristics of such different sources vary dramatically from one another and yet the network must provide a bandwidth and a quality of service guaranteed for each and every connection that is established across the network. It is therefore essential to provide a technique for characterizing the traffic on a high speed switching network which is, on the one hand, simple and easy to measure or calculate and, on the other hand, which captures all of the significant parameters of each of the widely diverse traffic sources.
Several standards bodies have heretofore proposed to characterize the traffic on each connection in a packet communications network utilize the following descriptors:
R: The peak pulse rate of the connection, in bits per second (bps). PA0 m: The mean pulse rate of the connection, in bits per second (bps). PA0 b: The duration of a burst period, in seconds.
These parameters are, for example, defined in CCITT Study Group XVIII, "Traffic Control and Resource Management in B-ISDN," CCITT Recommendation 1.371, February 1992, and CCITT Study Group XVIII, "Addendum to T1.606--"Frame Relaying Bearer Service . . . ", Recommendation T1S1/90-175R4, 1990. Bandwidth management procedures based on this set of traffic-characterizing parameters for operating a packet communications network are disclosed in "A Unified Approach to Bandwidth Allocation and Access Control in Fast Packet-Switched Networks," by R. Guerin and L. Gun Proceedings of the IEEE INFOCOM '92, Florence Italy, pages 1-12, May 1992, and the copending application Ser. No. 07/932,440, filed Aug. 19, 1992, and assigned to applicants' assignee.
These prior art bandwidth management techniques utilize these three descriptors to model user traffic by means of a two-state on/off fluid-flow model, by interpreting the b parameter as the average burst duration. In this model, the traffic source is either idle and generating no data, or active and transmitting data at its peak rate. It is assumed that the idle periods and the burst lengths are exponentially distributed and are independent from each other. Under these assumptions, the three descriptors R, m, and b have been used to characterize the source statistics and have been used to derive bandwidth management algorithms which are relatively easy to implement. When the idle periods and burst lengths are in fact exponentially distributed and independent from each other, these three descriptors do indeed fully characterize the source statistics and permit accurate bandwidth management.
Unfortunately, the actual user traffic offered to such packet communications systems is typically very complex and its impact on the performance of the network cannot be accurately predicted by the use of these three descriptors alone. Even when using the on/off fluid characterization of the traffic, the real traffic may have far more complex distributional characteristics than the simple exponential on/off model assumed in the prior art systems. In general, the burst lengths and the duration of the idle periods may have arbitrary distributions and may also have distributions which are correlated with each other. If these arbitrary, possibly correlated, distributions are not captured in the characterization of the traffic, the value and success of the bandwidth management procedures based upon the simplified exponential on/off model will be heavily impacted and may result in entirely inappropriate bandwidth management decisions. Furthermore, even if the actual traffic generation process does have exponential on and off time distributions which are independent from each other, the fluid-flow approximation ignores the microscopic stochastic representation of the underlying point process and focuses on the macroscopic correlations. That is, the fluid-flow approximation ignores such things as packet length distributions, inter-arrival time distributions within a burst, and so forth, and relies on such parameters as the length of the bursts and successive idle periods. With such a fluid-flow model, the same queuing behavior is obtained regardless of the packet length distributions. A more accurate (albeit more complex) characterization of the underlying point process will indeed show the effects of second order stochastic behavior on the queuing behavior of the packets at the switches in the network. A serious problem in the management of packet networks, therefore, is to better characterize the actual traffic process on the connections so as to permit more accurate and more useful management procedures.
In addition to requiring more accurate characterizations of the traffic entering a packet network, it is also necessary to identify the parameters of this characterization through simple procedures applied at the access point to the network. More specifically, it is necessary to provide a simple measurement technique for identifying parameters that accurately represent the essential characteristics of the actual traffic on a connection. Such characteristics must be available sufficiently rapidly that they can be used to drive the bandwidth management procedures which will produce useful results in time to operate the network.